1. Field of the Invention
The invention relates to a liquid crystal display device (LCD) having dual light units.
2. Description of the Related Art
In general, LCDs are flat panel display device having a relatively small size, slim profile, and low power consumption. Accordingly, LCDs find common use in mobile computers, such as notebook computers, office automation machines, and audio/video machines.
An LCD displays images by manipulating the transmission of light through a liquid crystal material by controlling an electric field induced through the liquid crystal material. The LCD does not necessarily emit the light by itself, but makes use of an external light source. Other display devices, such as electro-luminescences (ELs), cathode ray tubes (CRTs), and light emitting diodes (LEDs), emit light on their own.
LCDs can be generally classified into two different categories: transmission-type LCDs and reflective-type LCDs. A transmission-type LCD includes a liquid crystal panel having a liquid crystal layer interposed between two substrates. In addition, the transmission-type LCD includes a back light unit that supplies light to the liquid crystal panel. However, it is difficult to manufacture the transmission-type LCDs having slim profiles and light weight due to the volume and the weight of the back light unit. In addition, the back light unit requires large amounts of electrical power. This large electric power requirement shortens the amount of time a LCD computer notebook can run on battery power.
The reflective-type LCDs are not separately provided with light sources, but display images depending on natural (ambient) light conditions. The reflective-type LCDs thus do not require any additional light sources, and the reflective-type LCDs consume small amounts of electrical power and find wide employment in mobile display devices, such as electronic notes and personal digital assistants (PDAs). However, when the ambient light is insufficient, i.e. at night, the brightness level of the reflective LCDS decreases, whereby the information displayed cannot be read. Conventional methods of overcoming this problem of displaying images under dark conditions include installing a front light unit in the reflective LCDs.
FIG. 1 shows a perspective schematic diagram of a related art reflective-type LCD using a front light unit, and FIG. 2 shows a cross sectional view of the reflective-type LCD of FIG. 1. In FIGS. 1 and 2, a reflective LCD 100 includes a reflective liquid crystal panel 120, and a front light unit 110 positioned on the reflective liquid crystal panel 120 provides light. The reflective liquid crystal panel 120 is provided with a first substrate 121 and a second substrate 122, and a diffusing reflective electrode 123 is formed on the second substrate 122. The diffusing reflective electrode 123 reflects ambient light supplied from an upper surface of the reflective liquid crystal panel 120 or reflects incident light emitted from the front light unit 110.
The front light unit 110 includes a light source 111, a light guide plate 112, and a reflective mirror 113. The light source 111 generates light. The light guide plate 112 projects the light onto a display surface of the reflective liquid crystal panel 120. The reflective mirror 113 reflects the light generated from the light source 111 to the light guide plate 112.
FIG. 2 shows the upper surface of the light guide plate 112 being formed to have a prismatic configuration such that the light supplied from the light source 111 is reflected by an upper surface and a lower surface of the light guide plate 112. The light supplied to the light guide plate 112 is then supplied along a direction perpendicular to the reflective liquid crystal panel 120 positioned below the light guide plate 112. Next, the light supplied vertically to the reflective liquid crystal panel 120 is reflected by a reflective electrode 123 of the reflective liquid crystal panel 120, and the light travels upward over the light guide plate 110, thereby displaying an image. As a result, the related art technology produces a display that can only show an image on one side of the display.